This invention is related to the power generation industry and, more particularly, to the field of turbine generators and related methods.
Within the power generation industry, large-scale power generators convert mechanical energy, typically the energy output of a turbine, into electrical energy. The basic components of such power generators are a frame-supported stator core that provides a high permeability path for magnetism and a rotor assembly positioned to rotate continuously within the stator core so as to induce electrical current through rotor-borne conductors moving through magnetic fields set up within the stator. The resulting current is carried by high-current conductors through and out from a housing surrounding the power generator, to connectors that provide the current to a plant bus for power distribution to consumers, commercial establishments, and other users of electrical power.
It is common in the power generation industry to use 50 Hertz (Hz) or 60 Hz gas or steam turbines, e.g., using air or steam cooling, in power plants for different applications and particular for efficiency and power output issues. These 50 Hz and 60 Hz designs are often used in simple cycle power plants and in combined cycle power plants to provide higher levels for efficiency and power output. A simple cycle power plant, for example, is one where a gas turbine which drives a generator is the sole source of power generation. A combined cycle power plant, for example, uses gas turbine exhaust to create steam which is utilized by a steam turbine.
Separate frequencies, e.g., 50 Hz versus 60 Hz, often require separate components for each frequency. This can require additional manufacturing constraints, require additional inventory, and require an increase in changeover costs. To reduce product cost, it is desirable to reduce the number of parts produced so that the larger volumes of those parts produced can result in lower part cost and reduced tooling investment.
With 50 Hz and 60 Hz synchronous applications, the turbine is usually required to operate at the delivery current Hz, e.g., at 3000 revolutions per minute (rpm) or 50 revolutions per second (rps) for two-pole 50 Hz applications and 3600 rpm or 60 rps for two-pole 60 Hz applications. If the turbine is rotated at a frequency other than synchronous, e.g., due to frequency variations, the blades in a turbine element, e.g., a low pressure turbine element, may resonate at their natural frequency. Blading mechanical fatigue can then result with subsequent damage and failure. Such problems can be expensive and time consuming to repair and can cost down time for the power generation system.
In view of the foregoing, the present invention advantageously provides a single speed turbine generator that can be used in different power system output frequencies, e.g., either 50 Hz or 60 Hz, applications of a power generation system for power plants. The present invention also advantageously provides a power generation system and associated methods that allow the same turbine and generator to be used in both 50 Hz and 60 Hz applications. Because a turbine system, e.g., a turbine or a turbine with a gear box (hereinafter xe2x80x9ca turbinexe2x80x9d), and a generator rotor always rotate at substantially the same speed according to the present invention, variations in system frequency appear as variations in the generator rotor alternating current frequency so that the turbine still operates at the same frequency as the generator rotor even though variations in the system frequency may occur. Hence, in view of this, the present invention additionally advantageously provides a power generation system and associated methods that allows enhanced turbine design. The present invention further advantageously provides a power generation system, a power generator, and associated methods that have enhanced stability characteristics.
More particularly, a power generation system, to compensate for different power system output frequencies according to the present invention, preferably includes a turbine having a turbine rotor positioned to rotate at a preselected rotational frequency and a generator positioned to generate a power system electrical output current at a preselected power system output frequency. The generator preferably has a generator stator and a generator rotor positioned within the generator stator to induce electromotive force to the generator stator. The generator rotor preferably is coupled to the turbine rotor to be driven by the turbine rotor at substantially the same preselected rotational frequency. The generator rotor preferably has a rotor body and a plurality of generator coils mounted to the rotor body to induce electromotive force to the generator stator during rotation. The power generation system also preferably includes a frequency differentiator coupled to the generator rotor and connected to the power system electrical current output to differentiate between the preselected power system output frequency and the preselected rotational frequency of the generator rotor so that variations in the preselected power system frequency appear as variations in the generator rotor alternating electrical current frequency to thereby compensate for different preselected power system output frequencies.
According to the present invention, the frequency differentiator can advantageously be provided by an exciter or other frequency differentiation systems, such as an electronic cyclo-converter or other AC to AC, DC to AC, or AC to DC converter, as will be understood by those skilled in the art. An exciter, for example, of the present invention preferably has an exciter rotor coupled to the generator rotor to provide a magnitomotive force to the generator rotor during rotation at the same preselected rotational speed. The exciter rotor preferably has a rotating armature including at least one coil positioned thereon, and more preferably a plurality of coils with a three-phase alternating current field winding. The frequency differentiator also preferably includes an alternating current regulator positioned to receive unregulated electrical current from the power system electrical output current at the preselected power system output frequency and positioned to supply a regulated alternating current to one or more coils of the rotating armature of the exciter so that the electrical frequency of the one or more coils of the rotating armature substantially equals a difference between the preselected power system output frequency and the preselected rotational frequency. Advantageously, a portion, e.g., about 5 percent to about 20 percent, of the power system electrical current output of the power generation system is transferred to the generator stator from the generator rotor.
The present invention further advantageously provides a method of compensating for different power system output frequencies in a power generation system. The method preferably includes selecting a desired power system output frequency for a power generation system, selecting a desired rotational frequency of a generator rotor of a generator of the power generation system, and differentiating between the selected power system output frequency and the selected rotational frequency of the generator rotor so that variations in the preselected power system output frequency appear as variations in generator rotor alternating electrical current frequency to thereby compensate for different preselected power system output frequencies. The method can also include the power generation system having an exciter coupled to the generator rotor and rotating at the same selected rotational frequency, and the step of differentiating can include regulating alternating current received from the power system alternating current output and supplying the regulated alternating current to the exciter.
The frequency difference, e.g., 5 Hz, between the frequency of the power system output and the rotational frequency of the generator rotor or exciter, for example, can then be added to or subtracted from the generator rotor frequency, e.g., 55 Hz, to thereby produce the desired power generation system output frequency, e.g., 50 Hz or 60 Hz. Because the electrical frequency of the generator rotor compensates for power system swings, the power generation system of the present invention allows for enhanced stability characteristics for different power system output frequencies.